What DLC would rock the Forza world? Free DLC for adding features is my best guess. All these DLC cars we've had so far, for the most part, have had off road vehicles in them. The Ford Raptor, the Monster Suzuki, even this free Veloster Turbo from this week had a rally version of the car. So being logical here I'd peg a DLC (preferably free) that would rock the FM world would be to include off road racing. Maybe a Pike's Peak track (paved, unpaved, don't care either way) or a few offroad courses so we can properly use these offroad vehicles.
I would like Nurb24 w/night but I'm not a fan of night racing. Usually I stay away from that but to have it would be nice.
I don't think bringing in tracks that went MIA would be a world rocker, like the Bugatti Circuit or full Fujimi Kaido or those snake test tracks. But it would be awesome to have them back, especially via free DLC.